A printed circuit (PCB) on which a semiconductor device is mounted includes thermal vias for sinking heat generated from the semiconductor device mounted thereon. The heat is released out of the PCB through the thermal vias formed in the PCB.
The thermal vias are formed by filling through-holes formed in the PCB with copper, by way of employing, e.g., a dielectric layer stacked on a copper seed layer of the PCB. Before filling the through-holes with copper, the copper seed layer should be electrically charged. Electrons for electrically charging the copper seed layer are supplied to the copper seed layer through an electroless copper layer (dummy copper layer) provided on an inner wall surface of each of the through-holes. A package substrate (PKGSUB) machine controlling a Cu tank is used to fill the through-holes with copper and diffuse positively charged copper toward the copper seed layer within the through-holes (primary copper diffusion process). In the primary copper diffusion process, since the electroless copper layer and the copper seed layer are electrically charged by the electrons, the positively charged copper is attracted not only toward the copper seed layer but also toward the inner wall surface of each of the through-holes. In other words, the through-holes are not uniformly filled with copper by carrying out the primary copper diffusion process alone. For this reason, an additional copper diffusion process (secondary copper diffusion process) may be required in uniformly filling the through-holes with copper, entailing extra manufacturing time and cost. In particular, in case of forming thermal vias for a multi-layer PCB in which a plurality of dielectric layers are laminated on a copper seed layer, the manufacturing inefficiency may become even further aggravated because the primary and the secondary diffusion processes may need be carried out for each dielectric layer.
What is needed, therefore, is a PCB that overcomes at least the shortcomings of the known PCB discussed above.